Hydraulic power amplifier



May 12, 1970 H. KROHN ETAL HYDRAULIC POWER AMPLIFIER n a m V M 0 m a 6 mm w Q. mm mm n M M e R 2 MMN on o Filed Nov. 7. 1968 May 12, 1970 H. KROHN ETAL HYDRAULIC POWER AMPLIFIER 2 Sheets-Sheet 2 Filed Nov. 7. 1968 INVENTURS:

HOLGER KRUHN RAINER BARTH'ULUMKUS BYI 497mm i JA United States Patent 3,511,132 HYDRAULIC POWER AMPLIFIER Holger Krohn, Wombach, and Rainer Bartholomaus, Lohr am Main, Germany, assignors to G. L. Rexroth G.m.b.H., Lohr am Main, Germany Filed Nov. 7, 1968, Ser. No. 773,990 Claims priority, application Germany, Nov. 18, 1967, 1,650,521 Int. Cl. F15b 9/10, 15/17 U.S. Cl. 91375 15 Claims ABSTRACT OF THE DISCLOSURE A hydraulic power amplifier wherein a double-acting cylinder accommodates a reciprocable hollow differential piston dividing its interior into a first chamber which is connected with a source of pressurized hydraulic fluid and a second chamber. A rotary control plunger is installed in the piston and has a helical peripheral groove which is in permanent communication with the second chamber and can be placed into communication with a first port of the piston to thereby establish a flow of fluid between the two chambers so that the fluid displaces the piston in a direction to reduce the volume of the first chamber and the piston rod of the piston transmits motion to one or more driven devices. A second port of the piston can be placed into communication with the groove in response to appropriate angular displacement of the plunger and such second port then connects the second chamber with an outlet of the cylinder to permit escape of fluid from the second chamber with attendant movement of the piston in opposite direction.

BACKGROUND OF THE INVENTION The present invention relates to power amplifiers in general, and more particularly to improvements in hydraulic power amplifiers of the type wherein a piston is reciprocable in a double-acting cylinder to thereby effect axial displacement of one or more devices or parts in response to manipulation of a control system which establishes or terminates communication between the chambers of the cylinder as well as between one chamber and a receptacle which collects evacuated hydraulic fluid.

In presently known hydraulic power amplifiers of the above outlined character, the control system which regulates the flow of hydraulic fluid between the chambers of the double-acting cylinder as well as the evacuation of fluid from one of the chambers comprises a relatively large number of parts. Moreover, the axial length of the amplifier must be increased to accommodate the control system and the operation of the amplifier requires the flow of large quantities of hydraulic fluid.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a hydraulic power amplifier which is more compact, especially shorter, then presently known amplifiers, wherein the length of strokes of the working piston is substantially unaffected by the control system, and which is more accurate than conventional amplifiers.

Another object of the invention is to provide an amplifier wherein the length of strokes of the working piston can be regulated in a novel way, with utmost accuracy, and with a negligible delay following actuation of the control system.

"i ce The improved hydraulic amplifier comprises a doubleacting cylinder having an inlet for pressurized hydraulic fluid which can be supplied by a pump or the like and an outlet, a hollow differential working piston which is reciprocable in and divides the interior of the cylinder into a first chamber which communicates with the inlet and a second chamber, and a single control element which is rotatable in the piston and has a helical peripheral groove in communication with the second chamber. The piston has a smaller first surface which bounds a portion of the first chamber and a larger second surface which bounds a portion of the second chamber. A first port of the piston connects the first chamber with the groove in response to a first angular displacement of the control element so that the fluid can flow from the first into the second chamber to move the piston in a direction to reduce the volume of the first chamber whereby the piston rod of the piston effects an axial movement of a driven part or device until the piston moves its first port away from registry with the groove or until the control element assumes an angular position in which the first port is sealed from the groove. The piston is further provided with a second port which connects the second chamber with the outlet by way of the helical groove in response to a second angular displacement of the control element so that the piston rod moves in the opposite direction as long as the second port remains in communication with the groove.

The control element is preferably provided with a relatively wide and flat helical thread of rectangular or trapeziform cross-sectional outline. The thread defines the aforementioned helical groove and its top land is wide enough to completely seal one or both ports from the groove in response to appropriate angular displacement of the control element and/or in response to appropriate axial displacement of the piston.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved amplifier itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an axial sectional view of a hydraulic power amplifier which embodies the invention;

FIG. 2 is an enlarged view of a detail in the left-hand operation of FIG. 1; and

FIG. 3 is a transverse vertical sectional view as seen in the direction of arrows from the line IIl-III of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates a hydraulic power amplifier having a double-acting cylinder 1 provided with a first end wall or cover 2 and a second end wall or cover 3. The cylinder 1 accommodates a reciprocable hollow differential working piston 5 having a piston rod 6 which extends through a bore 7 in the cover 3 and is surrounded by a sealing ring 8 installed in an annular member *8a threaded into the cover 3. A second sealing ring 9 is received in an internal annular groove 10 of the annular member 8a. The piston rod "6 has an axial bore 11 the left-hand end of which extends through the piston 5 and receives a ported tubular member 14. The latter is provided with two radial ports 12, 13 (FIG. 2) and the right-hand portion of the bore 11 (as viewed in FIG. 1) accommodates a cylindrical guide 15. The right-hand end of the bore 11 is sealed by a plug 16 which maintains the guide in abutment with the tubular member 14. The left-hand end face 17 (FIG. 2) of the member 14 bears against a dished spring 18 which abuts against a split ring 19 installed in the piston 5. The bores 20, 21 of the tubular member 14 and guide 15 are coaxial and have identical diameters. These bores accommodate a control element or plunger 22 which is provided with flat external helical threads so that it resembles a feed screw. The left-hand end portion or extension 23 of the plunger 22 constitutes a torque-receiving stub which extends through a bore of the cover 2. The plunger 22 carries a split ring 24 which bears against the adjoining race of a thrust bearing 25 provided in the cover 2 and surrounding the stub 23. The bearing 25 holds the plunger 22 against axial movement in the cylinder 1. The left-hand end of an axial bore 26 in the control plunger 22 is sealed by a plug 27. The cover 2 is provided with an internal annular groove 28 which surrounds a portion of the stub 23 and communicates with the bore 26 of the plunger 22 by way of a radial bore 29 in the stub 23. A radial bore 30 in the cover 2 connects the groove 28 with an outlet 31 which is connected to a receptacle for hydraulic fluid. An annular sealing ring 32 is received in the cover 2 and is held in position by annular retainers, 33, 34 to seal the left-hand end of the annular groove 28.

The radial port 12 of the tubular member 14 communicates with an internal annular groove 35 of the piston 5 (see FIGS. 2 or 3). This piston is further provided with an axially extending bore 36 which communicates with the groove 35 and one end of which is sealed by a plug 37 adjacent to the dished spring 18. The other end of the bore 36 communicates with a first chamber 42 in the cylinder 1, i.e., the chamber 42 is in permanent communication with the port 12. The other port 13 of the tubular member 14 communicates with an annular space 38 between the internal surface of the piston rod 6 and the external surface of the guide 15. The member 14 comprises a smaller-diameter portion 39 and the clearance around this portion 39 constitutes a portion of the aforementioned space 38. The right-hand end of the space 38 is sealed by the plug 16. Radial bores 40 provided in the tubular guide 15 adjacent to the plug 16 connect the space 38 with a compartment 41 at the right-hand end of the plunger 22. The compartment 41 communicates with the axial bore 26 of the plunger 22. Thus, the port 13 is in permanent communication with the outlet 31 in each axial position of the piston 5.

In their neutral or zero positions, the radially innermost ends of the ports 12, 13 in the tubular member 14 are sealed by the threads of the plunger 22 (see FIG. 2

for the position of helical flanks 43, 44 on the threads of the plunger 22 in neutral positions of the ports 12, 13). This insures that the power amplifier operates with negligible clearance.

If the plunger 22 is rotated (for example, by way of an electric motor which can transmit torque to and turn the stub 23 stepwise), and depending on the direction of rotation of the plunger, the helical flanks 43, 44 of the thread on the plunger 22 expose larger or smaller portions of the ports 12, 13 in dependency on the inertia of the plunger to thus permit a flow of hydraulic fluid in predetermined directions. For example, and if the flank 43 exposes the port 12, fluid can flow from the first chamber 42 of the cylinder 1, through the axially parallel bore 36 of the piston 5, through the annular groove 35 in this piston, through the port 12, through the helical groove 45 of the plunger 22, and into a second chamber 46 provided in the cylinder 1 at the other axial end of the piston 5. The area of the surface 47 provided on the piston 5 and bounding a portion of the chamber 46 is greater than the area of a piston surface 48 which bounds a portion of the chamber 42; therefore, the piston 5 and reduces the volume of the first chamber 42. At the same time, the piston 5 begins to seal the port 12 from the groove 45.

When the rotation of the control plunger 22 is terminated, the piston 5 continues to move in a direction to the right, as viewed in FIG. 1, until the radially innermost end of the port 12 is sealed by the helical thread of the plunger 22. This seals the first chamber 42 from the second chamber 46 in the cylinder 1.

If the plunger 22 is thereupon rotated in the opposite direction, its thread exposes the innermost end of the port 13 to thus connect the second chamber 46 of the cylinder 1 with the receptacle for evacuated hydraulic fluid by way of the helical groove 45, port 13, annular groove 38, radial bores 40, compartment 41, axial bore 26, radial bore 29, annular groove 28, radial bore 30 and outlet 31. The outlet 31 is connected with the receptacle by a suitable return conduit, not shown. Since the pressure of fluid in the first chamber 42 exceeds the pressure of fluid in the chamber 46 which is then connected with the outlet 31, the piston 5 moves in a direction to the left, as viewed in FIG. l, to reduce the volume of the second chamber 46 so that the thread of the plunger 22 begins to seal the inner end of the port 13.

When the port 13 is sealed, the flow of fluid from the second chamber 46 into the receptacle by way of the outlet 31 is terminated and the piston 5 comes to a halt. It will be seen that each angular position of the plunger 22 corresponds to a certain axial position of the piston 5.

In order to insure proper centering of the plunger 22 in the tubular member 14, even when the port 12 or 13 communicates with the helical groove 45, the member 14 is provided with radial relief bores 49, 50 (FIG. 2). As shown in FIG. 3, the relief bores 49 communicate with the annular groove 35 and are located opposite the port 12. The relief bores 50 are located opposite the port 13 and communicate with the annular groove 38. The effective cross-sectional areas of bores '49, 50 correspond to those of the ports 12, 13 so that the plunger 22 is hydraulically balanced in the tubular member 14. The diameters of relief bores 49, 50 in the region adjacent to the top land 51 (FIG. 2) of helical thread on the plunger 22 are selected in such a way that they remain sealed by the top land 51 when the plunger turns in response to torque transmitted to its stub 23. The first chamber 42 of the cylinder 1 communicates with an inlet 31a (shown in FIG. 1) which admits pressurized hydraulic fluid in the direction indicated by arrow 52. The arrow 53 indicates the direction of outflow of fluid by way of the outlet 31.

It is c ear that the improved amplifier is susceptible of many modifications without departing from the spirit of the present invention. For example, the tubular member 14 with its ports 12, 13 can form an integral part of the piston 5 or piston rod 6. Furthermore, communication between the port 13 and the compartment 41 can be established by way of an axially parallel bore in the piston rod 6. Still further, the tubular guide 15 can be omitted if the parts 5, 6 are provided with a suitable axial bore for the plunger 22. For all practical purposes, the member 14 and the guide 15 form part of the working piston 5, i.e., it can be said that the ports 12, 13 are provided in the piston.

It will be seen that the control system of our power amplifier comprises a single control element (plunger 22) and a portion of the working piston 5 in contrast to conventional power amplifiers wherein the fluid flowing between the cylinder chambers or between one of the chambers and the outlet must pass through several additional control elements. The single control element occupies relatively little room. The axial length of the groove 45 in the periphery of the control element 22 corresponds to the length of the working stroke of the piston 5. By the simple expedient of rotating the element 22 with reference to the cylinder 1, the amplifier of our invention can ef fect amplification of power in axial direction of the cylinder.

In the aforementioned conventional power amplifiers, one control element must be provided with two sets of helical flanks and two separate passages for hydraulic fluid must be machined into the piston and its piston rod. Furthermore, and as mentioned above, the contro systems of such conventional power amplifiers must include several additional control elements as well as auxiliary channels which must be machined into the piston and/or piston rod to supply or evacuate hydraulic fluid. As a rule, the combined length of the piston and its piston rod in a conventional power amplifier is at least twice the length of the stroke-determining grooves or channels in the piston. Therefore, the useful volume of the cylinder is only half the useful volume of a normal cylinder.

Another important advantage of our power amplifier is that the pressurized fluid need not be admitted by way of the control system, i.e., that the inlet 31a can admit pressurized fluid directly into the chamber 42 of the cylinder 1. Also, a single helical flank (43 or 44) sufiices to regulate the flow of pressurized fluid between the groove 45 and the port 12 or 13. The lead of the groove 45 determines the relationship between the angu ar displacement of control element 22 and the axial displacement of piston 5, and such lead can be made small so that the overall length of the amplifier can be reduced accordingly. The machining of two instead of four helical flanks requires less time and thus reduces the overall cost of the apparatus.

As stated before, the thread on the control element 2 is preferably flat and of rectangular or trapeziform cross-sectional outline. The width of the top land 51 on the thread is selected in such a way that it can fully seal the inner ends of both radial ports 12, 13.

The pressure of fluid in the second chamber 46 of the cylinder 1 acts against the split ring 24 and thereby insures that the axial position of the control element 22 remains unchanged.

The diameter of that portion of the control element 22 which is received in the piston rod '6 is preferably less than the diameter of the stub 23. In this way, fluid in the chamber 46 can act against the shoulder at the righthand end of the stub 23 to further insure retention of the control element 22 in desired axial position with reference to the cylinder 1. Since the annular groove 28 of the end wall or cover 2 communicates with the outlet, proper sealing of this groove against leakage of fluid along the stub 23 presents no serious problems.

If the amplifier is to be used in a machine or apparatus wherein the part supporting the cylinder 1 is free to rotate with reference to the part or parts which are moved by the piston rod 6, the piston 5 and/or the cylinder 1 is provided with splines, keys or other suitable means which insure that the angular position of the piston with reference to the cylinder remains unchanged at all times. This is desirable to make sure that the ports 12, 13 can be placed in communication with or sealed from the groove 45 only in response to appropriate angular displacement of the control element 22 and commensurate axial displacement of the piston 5.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of our contribution to the art.

What is claimed as new and desired to be protected by letters Patent is set forth in the appended claims:

1. In a hydraulic power amplifier, a double-acting cylinder having an inlet for pressurized fluid and an outlet; a hollow differential piston reciprocable in an dividing the interior of said cylinder into a first chamber connected to said inlet and a second chamber, said piston having a smaller first and a larger second surface respectively bounding portions of said first and second chambers and a piston rod extending from said cylinder; and a control element rotatable in said piston and having a helical groove in communication with said second chamber, said piston having first port means connecting said groove with said first chamber in response to first angular displacements of said control element to thus effect movement of said piston in a direction to reduce the volume of said first chamber and second port means connecting said second chamber with said outlet in response to second angular displacements of said control element to thus effect movement of said piston in a direction to reduce the volume of said second chamber.

2. A structure as defined in claim 1, further comprising means for holding said control element against axial movement with reference to said cylinder, said control element comprising a torque-receiving portion extending axially beyond said cylinder.

3. A structure as defined in claim 1, wherein said piston rod extends axially through said first chamber.

4. A structure as defined in claim 1, wherein said control element is provided with a first helical flank which regulates the extent of communication between said groove and said first port means in response to said first angular displacements and a second helical flank which regulates the extent of communication between said groove and said first lport means in response to said second port means in response to said second angular displacements of said control element.

5. A structure as defined in claim 1, wherein said second port means is in permanent communication with said outlet.

'6. A structure as defined in claim 1, wherein said control element comprises a feed screw having a flat thread which defines said helical groove and a top land whose width exceeds the diameters of said port means so that said port means can be sealed by said thread.

7. A structure as defined in claim 6, wherein said thread is of rectangular cross-sectional outline.

8. A structure as defined in claim 6, wherein said thread is of trapeziform cross-sectional outline.

9. A structure as defined in claim :1, wherein said piston is provided with first and second relief bore means respectively communicating with and angularly spaced from said first and second port means and terminating at the periphery of said control element to insure uniform radial stressing of said control element.

10. A structure as defined in claim 1, further comprising thrust bearing means adjacent to said second chamber and arranged to hold said control element against axial movement with reference to said cylinder, said control element comprising a torque-receiving portion extending axially through said bearing means and outwardly beyond said cylinder.

11. A structure as defined in claim 1, wherein said piston rod is hollow and said control element comprises an elongated portion rotatably accommodated in said piston rod.

12. A structure as defined in claim 11, wherein said control element further comprises a torque-receiving second portion whose diameter exceeds the diameter of said elongated portion and which extends axially beyond said cylinder opposite said elongated portion.

13. A structure as defined in claim 1, wherein said piston rod is hollow and wherein said second port means communicates with said outlet by way of the interior of said piston rod.

14. A structure as defined in claim 1, wherein said cylinder comprises an end wall which is provided with said outlet and said control element comprises a torquereceiving portion extending outwardly through said end wall, said second port means communicating with said outlet by Way of bores provided in said control'element and in said piston.

11 5. A structure as defined in claim 1, wherein said piston is reciprocable in said cylinder in a predetermined unchanging angular position.

References Cited UNITED STATES PATENTS 2,171,005 8/ 1939 McNeil et a1. 91-375 8 2,994,304 8/1961 Shultz 91417 3,026,854 3/ 1962' Wiedmann et a1 91-375 3,106,224 10/1963 Moss et a1. 91375 PAU-L E. MASLOUSKY, Primary Examiner US. Cl. X.R. 

